1. Field of the Invention
The present invention relates to the heating and/or cooling of high power dissipating devices, such as semiconductor chips, and in particular, to a low pressure drop thermal device for microjet liquid impingement with distributed returns and methods of manufacturing the same.
2. Description of Related Art
It has been found that conventional thermal technologies for cooling electronic devices, such as, heat spreaders, heat sinks, and associated thermal interfaces, are generally not scalable to meet the demands of modern electronic devices. These modern electronic devices include those having increased power densities, operating frequencies and current leakages, as well as devices having small cooling fluid thermal budgets or having very high average power flux. For instance, in an electronic device having a high average power flux, a high power hot spot may dissipate 300 to 500 W/cm2, while a very high power hot spot may dissipate more than 500 W/cm2. Under such processing conditions, if the cooling method is primarily based on a heat conduction mechanism, the power flux will be undesirably large such that it generates significant thermal gradients along the cooling axis.
Due to the possibility of these significant thermal gradients along the cooling axis, acceptable cooling techniques typically require the use of a single-phase fast-forced convection and/or a two-phase evaporation based device with a circulating fluid. Yet, current higher cooling solutions often require a high fluid flow rate, which in turn, results in an undesirable increase in pressure drop on the cooler (fluid inlet to the outlet pressure difference). Also, known circulating cooling fluid solutions have a maximum operating pressure for preventing fluid leakage and mechanical damage to the system. As such, the extendibility of conventional cooling solutions is deleteriously limited by the pressure drop required to operate modern electronic devices having high power flux situations.
Prior art has focused on thermal structures having impinging liquid jets. For instance, FIG. 1 shows a conventional heating/cooling device 1. This thermal structure includes a perforated plate 6 having an array of fluid jets 4 that impinge orthogonally on a surface 3 of a substrate 2, such as a semiconductor chip or an interface between the jets and body to be cooled, and a lateral drain 5 for removing spent fluid. The fluid jet array 4 provides a high heat transfer rate when used to heat or cool the substrate surface 3, as compared to conventional convection heating and/or cooling processes.
In this scenario, the high kinetic energy of the array of fluid jets 4 provides fresh jet fluid in close proximity to the surface 3 in the region directly below the array of jets, generally at the center of the electronic component. This enables high heating or cooling rates at such regions. However, the high heating/cooling transfer rates decrease rapidly in areas of the surface 3 not residing directly below the surface area impinged by the jet fluid. This undesirably results in uneven cooling across the surface of the electronic component, especially from the center to the edge of the electronic component.
Conventional heating and/or cooling devices also commonly employ an array of fluid jets in combination with lateral drains 5. These lateral drains 5 are insufficient for cooling high power flux situations due to the lack of proper spent fluid drainage. In particular, the lateral drains 5 remove spent fluid in a radial flow pattern away from a fluid jet at the center of the surface. In so doing, the drain velocity increases approximately linearly with the number of fluid jet rows encountered from the central jet row(s) to the fluid drain outlet located at the periphery of such jet array, thereby reaching a maximum velocity at such periphery. Attempts have been made to resolve the resulting temperature gradient by placing the inlet fluid jets close to one another, but when these inlet microjets are placed too close together interactions between adjacent jets degrades the thermal performance of the array.
Current fluid jet arrays are also impractical for cooling high power flux situations due to their structural designs. Conventional single-phase jet array structural designs limit the drain velocity such that it does not exceed 50% of the fluid jet array velocity. Drain velocities above 50% of the fluid jet array velocity undesirably force the fluid jets to move away from the desired orthogonal orientation, thereby reducing the heat transfer rate by more than 20% relative to the heat transfer rate of a fully orthogonally oriented jet. This problem increases significantly in two-phase coolers, where the gas phase volumetric flow can be up to three orders of magnitude larger than the liquid flow.
Another disadvantage of conventional heating and/or cooling devices is that they do not protect the components on the semiconductor device in need of thermal management, such as, chips, interconnects, modules, integrated circuits, transistors, resistors, and the like, which reside on the semiconductor device surface opposite the surface being impinged.
In view of the foregoing, a need exists for improved methods of maximizing the heat transfer rate of fluid jet arrays for cooling/heating components having high power flux, which generate significant thermal gradients along the targeted surface, while controlling the pressure drop in the liquid cooling modules and protecting the critical semiconductor hierarchy in need of thermal management.